Yes, when you sell shares of a stock that you do not own, this is referred to as a short sale. You borrow the shares from a lender (like a broker-dealer) and sell in the open market with proceeds from the sale credited to your account. Eventually you must purchase the same number of shares borrowed and return them to the lender – this is referred to as closing out or covering the short-sale position. You must have a margin account in order to short stock. This is not a strategy for inexperienced investors.